The autumn equinox is now upon us! Today marks the moment that the sun crosses the celestial equator, ushering in the beginning of astronomical autumn in the northern hemisphere, which brings with it the inevitability of longer nights, perfect for stargazing.
In 2025, the autumn equinox will occur on Sept. 22 at 2:20 p.m. EDT (1820 GMT), when the sun moves southward across the celestial equator. The celestial equator is an imaginary projection of Earth’s equator into space, forming a circle around the sky that divides the northern and southern celestial hemispheres. The sun’s drop across the equator is due to a 23.5° tilt in Earth’s rotational axis, which shifts our star’s apparent path in the sky as our planet goes about its yearly orbit.
We experience two equinoxes each year, one in March and one in September, when the tilt of Earth is such that the sun shines equally on the north and south hemispheres. During an equinox day and night boast a roughly even 12-hour duration. It is for this characteristic that the name equinox was derived, from the Latin words “aequus” (equal) and “nox” (night).
On the day of the 2025 autumnal equinox, the sun rises almost exactly due east and sets to the west. The months that follow will see cooler temperatures set in as the northern hemisphere receives less direct sunlight, while the nights will grow longer and darker — a trend that will continue until we celebrate the winter solstice on Dec. 21.
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While Sept. 22 marks the beginning of autumn in the northern hemisphere, the exact opposite is true south of the equator, where spring is about to begin in earnest!
Dark, long autumn and winter nights are the perfect time to indulge in some astronomy. Be sure to check out our roundup of the best telescopes and binoculars available in 2025 to ensure that you’re ready to explore the changing skies.
Those interested in capturing the post-sunset realm should also read up on our selection of the most capable cameras and lenses for astrophotography, as well as our guide to photographing the moon as its seasonal path takes it higher in the night sky in the coming months.
Editor’s Note: If you would like to share your astrophotography with Space.com’s readers, then please send your photo(s), comments, and your name and location to spacephotos@space.com.
